Method and device for cutting a flat workpiece that consists of a brittle material

ABSTRACT

An arrangement for cutting a flat workpiece includes a drive unit for generating a relative movement between the focused laser beam ( 2 ) and the workpiece ( 1 ). The laser beam induces a thermomechanical stress in the workpiece along the cutting line. A scoring tool ( 7 ) generates an initial score at the start of the cutting line. A “flying” scoring is provided wherein a unit ( 5, 6, 8 ) moves the scoring tool ( 7 ). The unit is coupled in a controlled manner to the cutting movement of the laser beam ( 2 ) so that the scoring tool ( 7 ) can be brought into a short-time scoring working engagement with the workpiece ( 1 ) at the start of the cutting movement.

FIELD OF THE INVENTION

The invention relates to a method for cutting a flat workpiece made ofbrittle material, especially, glass or ceramic, with a laser beam bygenerating a relative movement between the laser beam and the flatworkpiece while moving the laser beam along a pregiven cutting line withinduction of a thermomechanical tension proceeding from a mechanicallygenerated initial score. A preferred application is the cutting of flat

BACKGROUND OF THE INVENTION

The invention relates further to an arrangement for cutting such a flatworkpiece by means of a laser beam.

Conventional separation methods for flat glass are based on firstgenerating a score in the glass utilizing a diamond or a cutting wheelin order to thereafter break the glass along the weakened locationgenerated in this manner by an external mechanical force. It isdisadvantageous with this method that particles (splinters) areseparated from the surface by scoring which can then deposit on theglass and there, for example, lead to scratches. Likewise, so-calledmarrings can arise at the cut edge which lead to an uneven glass edge.Furthermore, the microtears in the cut edge, which arise when scoring,lead to a reduced mechanical durability, that is, to an increased dangerof breakage.

An approach for avoiding splinters as well as surface fractures andmicrofissures comprises separating glass on the basis of thermallygenerated mechanical stress. Here, a heat source is directed onto theglass and is moved relative to the glass at a fixed speed and therebybuilds up a thermomechanical stress to such a high extent that the glassforms fissures. The necessary characteristic of the heat source to beable to position the thermal energy locally, that is, with an accuracyof better than a millimeter (which corresponds to the typical cutaccuracies) is satisfied by infrared radiators, especially gas burnersand especially lasers. Lasers have been proved and are in use because oftheir excellent focusability, good controllability of the power as wellas the possibility of the beam formation and therewith the intensitydistribution on the glass.

This laser cutting method induces a thermomechanical stress up to beyondthe resistance to breakage of the material via a local warming with thefocused laser beam in combination with a cooling from the outside. Thislaser cutting method is known from several publications. For example,reference is made to DE 43 05 107 C2.

This method distinguishes basically from the laser cutting methodsknown, for example, from EP 0 062 482 A1 or U.S. Pat. No. 5,120,926wherein a melting of the glass takes place while forming a cuttinggroove. The cutting groove is continuously blown clean by a gas.

The first-mentioned laser beam cutting method has proved itself as thesuperior method for different reasons and has prevailed in practice. Itis from this method that the invention proceeds.

Typically, a so-called start score or initial score is needed at thestart of the desired cutting line in that, typically, a weakenedlocation is generated mechanically on the glass surface or at the glassedge with a scoring tool, that is, a score is formed. Thethermomechanical stress, which is built up by the laser beam on thecutting line leads then to a break of the glass which proceeds from theweak location. The generation of this initial score is, for example,described in U.S. Pat. No. 4,044,936.

In the known case, the initial score is generated with an interruptedrelative movement between the laser beam and the flat workpiece to becut, that is, a “momentary standstill” in a scoring process which iscompletely separate in that the scoring tool is pressed with a pregivenmechanical force onto the glass surface.

The disadvantages of the known method are:

The duration of the cutting method is extended in each case by someseconds because an initial score must be generated in advance of eachlaser cut. Furthermore, the duration of forming the score is relativelylong so that the problem of damage of the glass with the formation ofsplinters arises.

SUMMARY OF THE INVENTION

The invention has the task to carry out the initially-mentioned methodand to configure the initially-mentioned arrangement in such a mannerthat the times for the cutting process are reduced and the danger ofdamaging the brittle material is very low.

The solution of this task is achieved with the method for cutting a flatworkpiece made of brittle material with a laser beam by generating arelative movement between the laser beam and the flat workpiece whilemoving the laser beam along a pregiven cutting line while inducing athermomechanical stress and proceeding from a mechanically generatedinitial score in accordance with the invention in that the initial scoreis generated coupled with the start cutting movement of the laser beam.

The arrangement for cutting a flat workpiece of brittle materialincludes a laser beam, a drive device for generating a relative movementbetween the focused laser beam and the flat workpiece while moving thelaser beam along a pregiven cutting line and with inducing athermomechanical stress and with a scoring tool for generating aninitial score at the start of the cutting line. With the above, thesolution of this task in accordance with the invention is achieved inthat a device for moving the scoring tool is provided which iscontrollably coupled in such a manner to the cutting movement of thelaser beam that the scoring tool can be brought into a short-termscoring action with the flat workpiece with the start of the cuttingmovement or shortly thereafter.

In the principle according to the invention, the initial score is“flyingly” generated without stopping the relative movement, that is, inthe same movement with which the cut by the laser beam occurs. In thisway, the advantages listed below result compared to a completelyseparate scoring process.

For each cut, a shortening of the process time of a few seconds results.

The damage to the glass is held extremely low because of the shortscoring duration which the “flying” scoring provides. In this way,splinters are avoided and the accuracy is increased.

DE 44 11 037 A 1 describes a method and an arrangement for separatingthe peripheral section of a rotating hollow glass during the manufacturethereof by means of a laser beam in combination with a mechanicallygenerated initial score. Here, first a thermomechanical stress along thecutting line is generated in the rotating hollow glass with the laserbeam and, only thereafter, a starting score is generated mechanicallyseparately from the laser beam. Accordingly, in the known case, thestart score is separately mechanically generated at any time without adirect coupling to the laser beam movement, for example, via a timecontrol and is not coupled to the start cutting movement of the laserbeam in advance of the laser beam cutting as in the invention.

The above-mentioned state of the art is in principle limited to thecutting of hollow glass where there is no start and no end of thecutting line. In contrast, the invention relates to the cutting of flatglass wherein the one edge defines the start and the other edge definesthe end of the cutting line. The described problem of the interruptionof the laser beam movement to set the starting score occurs only for aflat workpiece across which the laser beam is moved transversely in theinitially-described state of the art and this led to the “flying”scoring in accordance with the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will now be described with reference to the single FIGUREof the drawing showing an arrangement according to the invention forcutting a flat workpiece made of a brittle material.

DESCRIPTION OF THE PREFERRED EMBODIMENTS OF THE INVENTION

A flat glass substrate 1 is to be cut by a laser beam 2 of a laserscanner 3 along a pregiven cutting line.

The corresponding arrangements are known, for example, from thepublications mentioned initially herein and therefore do not have to beexplained here further. A relative movement is present between the laserbeam 2 and the glass substrate 1 along the given cutting direction.Typically, the glass substrate is fixed in position and the laser beam 2is moved. Conversely, the laser beam 2 can be fixed and the glasssubstrate 2 moved.

A solenoid 5 is connected to the scanner 3 in a controlling manner viathe symbolically shown connection 4. The solenoid 5 has a switching flag6 which can be moved upwardly or downwardly as indicated by arrows independence upon the drive of the solenoid 5. A scoring tool 7 is mountedat the lower end of the switching flag 6 facing the glass substrate andis, for example, a hard metal wheel. A position sensor 8 is assigned tothe switching flag 6 at a suitable location. The output signal of theposition sensor 8 is switched to the control input of the solenoid 5 asindicated by the broken line.

The “flying” scoring according to the invention functions as follows.The hard metal wheel 7 is moved with the start of the cutting movementagainst the edge of the glass substrate 1. When the wheel 7 touches theedge, the wheel experiences a slight displacing movement of maximally 1mm. This relative position change of the wheel is detected by the sensor8 and then a rapid lifting of the wheel by approximately 5 mm istriggered by means of the solenoid 5 via the control.

The lifting takes place in a time range of approximately 0 to 2 seconds.

The stroke movement of the scoring tool can also take place via ahydraulic or pneumatic actuator. The advantage of the solenoid, however,lies in its rapid reaction time.

The damage to the glass is held so low by the “flying” scoring accordingto the invention that the damage is not detectable by the unaided eye.

The essence of the invention is in the “flying” scoring, that is, ascoring in one movement with the laser cut. This scoring functions thefastest as described in the illustrated example; however, it can berealized in a slower sequence (but always still in the cutting movement)and also differently (for example, in the case that the scoring tooldoes not have a switching flag and is moved only by a control signal).

1. A method for cutting a flat workpiece made of brittle material alonga cutting line, the method comprising the steps of: providing a scoringtool and a focused laser beam aligned with respect to said cutting line;generating a relative movement between said focused laser beam and saidflat workpiece; imparting an initial score to said flat workpiece at theupper side edge thereof at the start of said cutting line with thescoring of said flat workpiece being coupled to a start of said movementfor cutting said flat workpiece; automatically raising said scoring toolby a predetermined stroke distance after scoring said edge therebyscoring said flat workpiece only at said upper side edge; and, movingsaid focused laser beam along said cutting line so that said scoringtakes place in one movement with the laser cutting and said focusedlaser beam then inducing a thermomechanical stress along said cuttingline greater than the breaking strength of said flat workpiece.
 2. Themethod of claim 1, wherein the raising of said scoring tool takes placein a time interval of up to two seconds.
 3. The method of claim 1,wherein said relative movement is generated by moving said laser beamalong said cutting line utilizing a laser scanner.
 4. An arrangement forcutting a flat workpiece made of a brittle material along a pregivencutting line, the arrangement comprising: means for directing a focusedlaser beam onto said cutting line; a drive for generating a relativemovement between said laser beam and said flat workpiece for guidingsaid focused laser beam along said pregiven cutting line so as to inducea thermomechanical stress in said workpiece greater than the breakingstrength thereof along said cutting line; a scoring tool for impartingan initial score to said workpiece at the start of said cutting linewith the scoring of said flat workpiece being coupled to a start of saidmovement for cutting said flat workpiece; said scoring tool beingmounted next to the upper edge of said workpiece; a device for rapidlylifting said scoring tool and said device being coupled to the cuttingmovement so that, at the start of the cutting movement or shortlythereafter compared to the total cutting time, said scoring tool is inoperative contact with said flat workpiece for imparting said initialscore thereto and then is rapidly raised.
 5. The arrangement of claim 4,said device including a solenoid having a control input; said solenoidincluding a switching flag movable between a first position and a secondposition and said switching flag including an end for accommodating saidscoring tool thereon; said device further including a position sensorfor detecting said second position and for outputting a signal to saidcontrol input when said second position is detected; and, means forcontrolling said solenoid so that, after said scoring tool is moved by acorresponding movement of said switching flag at the start of thecutting movement against the edge of the workpiece and a verticalposition change of the switching flag is triggered an activation of thesolenoid takes place via said output signal of said position sensor andtherewith a rapid lifting of the switching flag with the scoring tool.6. The arrangement of claim 4, said device being formed by a hydraulicor pneumatic actuator.